1. Technical Field
The present invention relates to check valves and, more particularly, to a check valve capable of reducing pressure losses in comparison to conventional check valves and hence capable of greatly reducing the fluid pressure reduction at the downstream side.
2. Background Art
There has heretofore been proposed a spring-loaded check valve in which a valving element is urged toward a valve seat by a compression spring or other urging member, and when the supply of fluid is stopped, the valving element is pressed against the valve seat by the force of the spring to prevent back flow.
In the conventional check valve of this type, the valving element is urged toward the valve seat by using a spring as stated above. Therefore, it is necessary in order to open the valve to move the valving element by compressing the spring. Incidentally, when fluid flows through a pipe, pressure losses are produced by pipe friction occurring between the fluid and the pipe wall and a turbulent flow generated by an object put in the flow. If a check valve is installed, the flow path area is reduced to a considerable extent when fluid flows between the valving element and the valve seat. As a result, the pipe friction increases. In general, there is a large change in configuration at the rear side of the valving element. Therefore, a turbulent flow is generated at the rear side of the valving element. The valve opening of the valving element is determined by a differential pressure caused by these pressure losses, i.e. a difference between pressures acting on the upstream and downstream sides of the valving element. In this regard, large pressure losses require a correspondingly large amount of energy to send fluid in the forward direction, for example. Accordingly, how to reduce these pressure losses has been an issue for many years, and various schemes have heretofore been proposed.
Japanese Patent Application Publication No. Hei 10-288265 discloses one example of such conventional schemes. In the invention disclosed in this JP publication, a main valving element and an auxiliary valving element are provided and acted upon by respective springs serving as urging members, and a rectifying passage is provided for each of the two valving elements to reduce the occurrence of turbulent flow, thereby reducing the pressure losses. In this case, however, the cross-sectional area of the rectifying passage is small. Therefore, when fluid flowing through the rectifying passage enters a valve chamber having a much larger cross-sectional area than the rectifying passage, the flow of fluid is disordered to a considerable extent, resulting in a turbulent flow. Because the auxiliary valving element is a plate-shaped member, a friction occurs when fluid flows between the valve seat and the valving element, and a turbulent flow is generated when fluid flows toward the rear of the valving element. Thus, the invention disclosed in Japanese Patent Application Publication No. Hei 10-288265 cannot be said to have attained a satisfactory reduction of pressure losses.